Thioglycerol derivatives and their use in polysulfide compositions for optical material

ABSTRACT

Novel thioglycerol derivatives, processes for their manufacture, and optical materials made from such compounds. The thioglycerol derivatives have high concentrations of sulfur relative to compounds conventionally used for optical materials, and thus exhibit high refractive indices without sacrificing processability.

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/978,759 filed Nov. 26, 1997 now U.S. Pat. No. 5,973,192.

BACKGROUND OF THE INVENTION

The present invention is directed to thioglycerol derivatives and theirpreparation, the derivatives having utility in optical materials such aslenses.

Plastic lenses for use in eyeglasses and cameras have become widespreadin view of their lightweight, durability, dyeability and workability ascompared to conventional glass lenses. Resin compositions suitable forthe manufacture of optical lenses must possess certain characteristics,including a high refractive index, high surface accuracy, low dispersionproperties and good heat resistance, impact resistance and scratchresistance. Diethylene glycol bis(allylcarbonate (DAC) andpolycarbonates have conventionally been used for plastic lenses. Lensesmade of DAC, however, have lower refractive indices than lenses made ofglass of a corresponding overall thickness, and therefore do not performas well in this regard.

U.S. Pat. Nos. 4,775,733 and 5,191,055 disclose polyurethane lenses madeof a polymer between a xylylene diisocyanate compound and a polythiolcompound having a higher refractive index than lenses made from DAC.However, such lenses generally suffer from poor heat resistance,hindering the ability to use high temperatures during heat treatmentprocessing steps.

It therefore would be desirable to develop compositions for use inmaking optical materials that do not suffer from the various drawbacksmentioned above, and that have good machinability and processability.

SUMMARY OF THE INVENTION

The problems of the prior art have been overcome by the presentinvention, which provides novel thioglycerol derivatives, processes fortheir manufacture, and optical materials made from such compounds. Thethioglycerol derivatives have high concentrations of sulfur relative tocompounds conventionally used for optical materials, and thus exhibithigh refractive indices without sacrificing important properties such asprocessability.

DETAILED DESCRIPTION OF THE INVENTION

Thioglycerol (HSCH₂ CH(OH)CH₂ OH) and 1,3-dimercapto-2-propanol are thebases of the compounds of the present invention. They can beconveniently esterified with common mercaptoacids of the formulaHS(CH₂)_(n) COOH wherein n is from 1 to 5, including thioglycolic acid,3-mercaptopropionic acid, etc., to form compounds having the followinggeneric formula: ##STR1## wherein X is --SH or X═--SH, ##STR2## and n isfrom 1 to 5. Those skilled in the art will appreciate that as the chainlength of the mercapto acid increases (i.e., as n increases from 1 to 5and beyond), the percent sulfur in the composition decreases, therebydecreasing the refractive index of the resulting derivative.Accordingly, esterification with thioglycolic acid is especiallypreferred, in particular with two equivalents of thioglycolic acid,resulting in thioglycerol bismercaptoacetate (TGBMA) having thefollowing formula: ##STR3## In addition, the resulting TGBMA derivativecan be further oxidized, such as with peroxide or other suitableoxidizing agents known to those skilled in the art, to give varyingdegrees of disulfide. Such disulfides, which can include dimers, trimersand oligomers, can be represented by the following generic formula:##STR4## wherein R₁, R₂ and R₃ may be the same or different and areindependently selected from hydrogen, ##STR5## wherein R' is hydrogen orR₁. Examples of such disulfides are shown below: ##STR6## The trimersand oligomers are formed by further oxidation of the mercaptans of thedimers. The higher molecular weight materials result in an increase inthe refractive index. Moreover, as the reaction medium continues to beheated, the refractive index increases. Accordingly, one can control therefractive index by controlling the heating of the reaction. Theresulting product is a complex mixture of any of the foregoingstructures.

The esterified product can be washed with a suitable base, preferablyammonia or alkali metal hydroxide, such as sodium or potassiumhydroxide, to remove any residual mercaptoacid. The present inventorsalso have found that limiting the wash step also limits the refractiveindex of the final product. More specifically, washing the product withbase, preferably ammonia, has a drammatic effect on the refractiveindex. Thus, by limiting the washing step, the refractive index can bekept at a predetermined level (if the refractive index is too high, theproduct is not compatible with other components).

In an alternative embodiment, thioglycerol is oxidized to thecorresponding disulfide with a suitable oxidizing agent: ##STR7## Thisresulting tetraol can be readily esterified with the aforementionedmercaptoacids to form a highly functionalized mercaptan having a sulfurcontent slightly higher than thioglycerol bismercaptoacetate: ##STR8##

In a further embodiment of the present invention,1,3-dimercapto-2-propanol is esterified with thioglycolic acid toproduce dimercaptopropanol mercaptoacetate. Disulfides of thismercaptoacetate can be produced by analgous procedures to those above,resulting in the following derivatives: ##STR9##

Optical materials such as lenses can be prepared from the derivatives ofthe present invention by conventional means. Suitable additives such assurface active agents may be used. The resulting lens may be subjectedas necessary to various physical and chemical treatments such as surfacepolishing, treatment for antistaticity, hard coat treatment,non-reflecting coat treatment, dyeing, treatment for photochromism,etc., all well known to those skilled in the art.

The invention is further illustrated by the following non-limitingexamples.

EXAMPLE 1

In a 5 liter, 3 neck roundbottom flask equipped with a magnetic stirrer,thermocouple and a distillation head with vacuum take off, is placedthioglycerol (1994.60 g, 7.78 moles) and thioglycolic acid (2332.96 g,24.82 moles).

Methane sulfonic acid (14.16 g, 0.15 mole) is added, vacuum applied(5-10 mm Hg) and the reaction heated to 70° C. When the reactiontemperature reached about 40° C., water began to distill over. Thereaction was heated at 70° C. for 4-5 hours and cooled to roomtemperature. The reaction is then transferred to a 6 liter Erlenmeyerflask which is equipped with an overhead stirrer.

Aqueous ammonia (4218.00 g, 5%, 12.41 moles) was added and the reactionstirred for 30-45 minutes. An exotherm occurs to approximately 35-40° C.upon addition of the ammonia. This can be controlled by cooling thereaction to 10-15° C. prior to the addition of ammonia. The upperammonia layer is then removed and the reaction washed with a 3×2 litersof water. After washing is completed, the reaction is stripped waterfree, either via a vacuum distillation or on the rotary evaporator toyield 1994.6 g, 69%, of TGBMA as a light yellow oil. The refractiveindex was 1.5825.

EXAMPLE 2

To a 250 ml, three neck flask equipped with a condenser, thermometer,magnetic stirring, and a constant addition funnel was added thioglycerol(42.00 g, 0.39 mole), water (32.40 g, 1.80 mole) and ferrous sulfate(0.02 g, 0.3 mmole). Hydrogen peroxide (42.00 g, 0.30 moles) was addedslowly, maintaining a temperature of less than 50° C. Care was taken notto add the hydrogen peroxide too rapidly, thereby avoiding theaccumulation of excess peroxide.

The reaction mixture was extracted with methyl isobutyl ketone to removeunreacted thioglycerol. The aqueous portion was concentrated to dryness,after testing for unreacted peroxide, resulting in 41.90 g of thedisulfide product (>99% yield). The refractive index was 1.5670.

EXAMPLE 3

Dithioglycerol tetramercaptoacetate was prepared using the proceduredescribed in Example 1 after adjusting the stoichiometry.

EXAMPLE 4

1,3-Dimercapto-2-propanol (12.8 g, 0.1 moles), thioglycolic acid (9.5 g,0.1 moles) and methane sulfonic acid (0.13 g, 1.30 mmoles) were combinedand heated to 70° C. under about 4 mm of vacuum. The reaction mixturewas held at this temperature and pressure for 2-3 hours until the waterwas distilled from the reaction. The reaction completion can bemonitored by titration for acid number.

The reaction was washed with a 3.7% aqueous ammonia followed by one ortwo water washed to remove the excess thioglycolic acid. The finalproduct was stripped to dryness resulting in a 79% yield. The refractiveindex was 1.6200.

EXAMPLE 5

In a 5 liter, 3 neck round bottom flask equipped with a magneticstirrer, thermocouple and a distillation head with vacuum take off, isplaced thioglycerol (1000.00 g, 9.26 moles), thioglycolic acid (1874.07g, 20.37 moles) and methane sulfonic acid (11.52 g, 0.12 moles). Vacuumis applied (5-10 mm Hg) and the reaction heated to 70° C. The reactionwas heated at 70° C. for 3-4 hours at which time the crude refractiveindex is 1.5500. After additional heating for 2-3 hours, which raisesthe crude refractive index to 1.5610, the reaction is cooled andtransferred to a 6 liter Erlenmeyer flask equipped with an overheadstirrer.

Aqueous ammonima (2361.3 g, 5%, 6.95 moles) was added to the Erlenmeyerflask and the reaction stirred for 30-60 minutes. An exotherm occurs toapproximately 35-40° C. upon addition of ammonia, Cooling the reactionto 10-15° C. prior to ammonia addition can control the exotherm. Theupper ammonia layer is then removed and the reaction washed with 3×2liters of water. After washing is completed, the reaction is strippedwater free, either by vacuum distillation or rotary evaporator to yield1777.9 g, 75% of TGBMA as a light yellow oil. The refractive index hasnow increased to 1.5825 from the crude refractive index of 1.5610.

What is claimed is:
 1. A thioglycerol derivative having the followingformula: ##STR10## wherein R₁, R₂ and R₃ may be the same or differentand are independently selected from hydrogen, ##STR11## wherein R' ishydrogen or R₁, with the proviso that R₁, R₂ and R₃ do not all representhydrogen.
 2. A thioglycerol derivative selected from the groupconsisting of the following compounds or a mixture thereof: ##STR12## 3.A plastic lens comprising the thioglycerol derivative of claim
 1. 4. Aplastic lens comprising the thioglycerol derivative of claim 2.